1. Field of the Invention
This invention relates to a method of making a thermal management material for a circuit board panel, printed circuits formed thereon and circuit boards cut therefrom.
2. Prior Art Statement
Light emitting diodes, LED's, are beginning to replace conventional lighting in many applications. With the development and increasing use of these high-energy output devices, problems with the assembly of the electrical components to the circuit board are increasing. This is primarily due to the excess heat that is generated during the LED operation and thus the necessity to use circuit boards containing a metal heat sink. The metal heat sink is then used for thermal management of the circuit by pulling the heat away from the component during operation. Presently available material, while more than able to dissipate the heat of the component presents assembly issues during the soldering of the LED. At the temperatures sufficient to produce an acceptable solder joint, the temperature of the component during soldering may approach a point where harm to the component occurs or the integrity of the adhesive junction between the electrically insulating material and the heat sink is damaged. It is believed that a certain amount of acid may be generated at the interface of the electrically insulating material and the heat sink because the surface of the heat sink at the time of lamination is not completely inert.
It is known to provide a method of preparing a circuit board from a laminate of dielectric material sandwiched between layers of copper and aluminum comprising the steps of forming at least one through hole in the laminate, anodizing the exposed areas of the aluminum layer in an anodizing solution while electrically isolating the aluminum from the copper, electroplating a conductive metal over the anodized coating, etching exposed areas of the dielectric material and electro-less plating a conductive metal coating over all exposed surfaces of the laminate. For instance, see the U.S. Pat. No. 4,525,247 issued on Jun. 25, 1985, to Rodger P. McMonagle. Circuit boards prepared from panels produced by the above method have been suitable for low temperature applications, however, it has been found that delamination of the dielectric material from the aluminum is prevalent in applications wherein the temperature at the interface between the dielectric and the aluminum exceeds approximately 100 degrees Centigrade and thus thermal management of the panel is limited. Often, delamination occurs during mounting of circuit components as the solder temperature is often 250 degrees Centigrade or higher.
It is also known to provide a printed circuit board comprising a laminated metal substrate designed for dissipating heat having a curable dielectric material located on the substrate, wells in the dielectric material contacting the substrate created by masking the curable dielectric material at the location of the wells, the wells further having active circuit components mounted therein which contact the substrate, the laminated metal substrate having a coefficient of thermal expansion which matches that of the active circuit components. For instance, see the U.S. Pat. No. 4,999,740 issued on Mar. 12, 1991 to Ilardi, et al. Thus, though thermal management of a circuit is achieved by removing the dielectric material in the area of heat generating circuit components, it has been found that delamination of the dielectric material from the substrate still occurs in high ambient operating temperatures and/or during solder mounting of circuit components.
It is further known to provide a method of manufacturing an electrically driven LED lamp assembly comprising the steps of disposing an electrically insulating coating of less than 1000 microns thickness over an electrically and thermally conductive, entirely metal heat sink, printing circuit traces on the coating and adhesively securing light emitting diodes to the circuit traces with an electrically and thermally conductive adhesive. For instance, see U.S. Pat. No. 5,857,767 issued on Jan. 12, 1999 to Peter A. Hochstein. Hochstein provides thermal management of circuit assemblies by avoiding the soldering of components to the circuit board, however it has been found that delamination of the dielectric material from the substrate may still occur in high ambient operating temperatures, particularly where the L. E. D. lamp assembly is confined to a small volume.
Also known is to provide a circuit board panel comprising a copper or aluminum substrate, a layer of epoxy and a layer of copper wherein the layer of epoxy contains finely comminuted, thermally conductive, electrically insulating material such as a ceramic material. For instance, see the technical bulletin entitled Thermal Clad© Overview available on the website of The Bergquist Company. Though thermal management of a circuit board is enhanced by providing thermally conductive material in the layer of epoxy, delamination of the circuit board may still occur at the interface between the epoxy and the substrate in high temperature applications or when applying components to the circuit board.
Finally, it is known by the inventors hereof to prepare a metal surface for painting by conditioning the metal surface with a metal cleaner.